RESUMEN

Precambrian filamentous microfossils are common and diverse. Nevertheless, their taxonomic assignment can be difficult owing to their overall simple shapes typically lacking in diagnostic features. Here, we report in situ communities of well-preserved, large filamentous impressions from the Ediacaran Itajaí Basin (ca 563 Ma) of Brazil. The filaments are uniserial (unbranched) and can reach up to 200 µm in width and up to 44 mm in length. They occur as both densely packed or sparsely populated surfaces, and typically show a consistent orientation. Although simple in shape, their preferred orientation suggests they were tethered to the seafloor, and their overall flexibility (e.g. bent, folded and twisted) supports a biological (rather than sedimentary) affinity. Biometric comparisons with modern filamentous groups further support their biological affinity, suggesting links with either large sulfide-oxidizing bacteria (SOB) or eukaryotes. Other morphological and palaeoecological characteristics further corroborates their similarities with modern large filamentous SOB. Their widespread occurrence and association with complex Ediacaran macrobiota (e.g. frondose organisms, Palaeopascichnus) suggest that they probably played an important role in the ecological dynamics of these early benthic communities by providing firm substrates for metazoans to inhabit. It is further hypothesized that the dynamic redox condition in the latest Ediacaran, with the non-continuous rise in oxygen concentration and periods of hypoxia, may have created ideal conditions for SOB to thrive.

Asunto(s)

Eucariontes , Fósiles , Bacterias , Brasil , Oxidación-Reducción

RESUMEN

We report the first occurrence of microfossils in Ediacaran strata of the Camaquã Basin. The assemblage includes simple (Leiosphaeridia sp. predominantly) and ornamented acritarchs associated with microbial mats. They are related to the Ediacaran Complex Acanthomorph Palynoflora (ECAP) and Late Ediacaran Leiosphere Palynoflora (LELP) due to the similar morphology and time interval assigned to those assemblages, though the observed specimens are a lot simpler and less diversified. However, different from the usual occurrences, this case study reports Neoproterozoic cosmopolitan communities living in marine (basal unit) and lacustrine (middle units) settings. Fossils within non-marine strata in the Precambrian record are rare. Therefore, this first finding of microfossils in the Camaquã Basin constitutes a new piece of the puzzle related to the history of the Panafrican-Brasiliano basins and shed some light on possible settings where the Ediacaran eukaryotes have evolved.